Never go more than two weeks without putting your product ideas in front of real users and customers.

You’ve worked hard, you’ve generated a compelling business case, you’ve spent time designing and writing specs, you’ve solicited the input from a number of customers and stakeholders, you’ve answered countless questions from the developers, and you finally launch.

Yet the product fails

It’s either something that the customers just didn’t want once they saw it, or they couldn’t figure out how to use it, or it would have taken so long to build that you were forced to gut it just to get it shipped in a reasonable time frame.

It may have failed due to any number of issues:

Your customers didn’t really want what they thought they wanted; you didn’t have capable designers; you were confusing yourself with your customer; you didn’t get engineering’s input until it was too late; or one hundred other reasons.

But all of these would have been preventable if you had just been able to get the product concept in front of real users early enough in the process to have determined if the product was destined to succeed or fail.

A lot of people think the only way to get this feedback is to design it, build it, launch it, and then see what happens.

There are a few cases where that’s true, but it’s rare. For the most part, especially for Web products, we can, in fact, get the feedback we need in the time frame we need it, if we focus on the right activities—prototyping and testing that prototype on real users—rather than spending our time creating business cases, gathering requirements, and writing specs.

But another less obvious dynamic happens when we wait too long to get feedback from real users and customers: we get too attached to our own ideas.

Many product managers hold off for months before they get any real validation of the ideas with the people that matter.

And every day that goes by the product team gets increasingly deeper and more entangled with their original idea to the point that now they’re either too scared to show it to customers for fear of having to start over, or they are so confident that it will be great that they think they can just skip to development, or they’ve got developers screaming at them just to give them something to build.

So for those people that believe in the principle that they need to validate their product ideas with real users, but are unsure of how “baked” the idea needs to be, I offer this very explicit rule—never go more than two weeks without putting your product ideas in front of real users and customers.

Does this mean your ideas won’t be fully fleshed out yet? Yes, and good.

Does this mean that customers might not like your ideas? Yes, and good.

Remember, it’s all about failing fast.

You can and should continue to refine your product ideas—it’s not like you have two weeks to define every last pixel. But you must get out of the office and put your ideas in front of real users while you still have time to adapt.

At Facebook they like the mantra, “Don’t fall in love,” as a way to ensure that the product team doesn’t get so enamored of their own ideas that they ignore or rationalize the feedback from the people that matter.

Steve Blank has a great line about this: “In a startup, no facts exist inside the building, only opinions.” I believe strongly that the most important thing that a product manager must do is put his ideas in front of real users and watch their responses.

Remember that your job as a product manager is to define a successful product and have evidence that the product will be successful, not just your opinion. And you won’t find that evidence inside your building.